1. Field of the Invention
This invention generally relates to fuel delivery methods and apparatus and more particularly to an apparatus providing a variable venturi throttle and a method for dispersing a fuel-air mixture into an intake airstream for an internal combustion engine.
2. Brief Description of Prior Art
The typical carburetor is the conventional mechanism for delivering fuel to an internal combustion engine. The typical carburetor mixes a quantity of fuel from a main discharge with a quantity of air flowing through a fixed venturi, as a result of a low pressure created by the air flowing through the fixed venturi which draws the fuel into the air. A circular-shaped, butterfly valve positioned in a cylindrical throttle opening in a carburetor throttle plate controls the amount of fuel-air mixture delivered to the engine. The butterfly valve is pivoted about its diametric axis in the throttle opening to control the speed and power output of the engine. Positioned in its maximum transverse orientation across the throttle opening, very little fuel and air mixture from the fixed venturi is allowed to enter the engine. As the butterfly valve opens, crescent shaped openings are formed between the circular edges of the butterfly valve and the circular inner wall of the throttle opening to allow an increasing air flow therethrough. In its maximally opened position, the butterfly valve is aligned parallel with the axis of the throttle opening to minimally restrict the airflow therethrough.
Since the butterfly valve is essentially closed when the engine idles or runs very slowly, a supply of idle fuel is delivered directly into the engine manifold from a position downstream of the butterfly valve, with respect to the normal flow path through the carburetor, to support combustion and engine operation. However, even when the butterfly valve is open, the idle fuel is still typically supplied. Upon rapidly opening the butterfly valve, an accelerator pump injects raw fuel directly into the rapidly increasing airstream through the butterfly valve until the fixed venturi can supply sufficient fuel to support the increased engine power requirements.
Although usually reliable in operation, a number of problems with conventional carburetors have prevented attaining the best fuel consumption economy and the best reduction in pollutant emissions. These problems result in substantial measure from the construction and arrangement of the previously described elements in the typical carburetor. In controlling the amount of fuel-air mixture delivered to the engine, the butterfly valve creates significant alternations of the desired fuel-air mixture under different engine operating conditions. When the throttle valve is closed after the engine has been running at a relatively high speed, the high vacuum created by the slowing engine tends to cause a build-up or pocket of accumulated fuel at the butterfly valve, thereby significantly enriching the mixture and causing an adverse effect on pollutant emissions, particularly on hydrocarbon emissions, since the larger fuel droplets do not completely burn or combust. With the butterfly valve partially open, the fuel-air mixture flowing through the crescent shaped openings is subject to somewhat radical changes in flow stream characteristics. The flow stream changes and vacuum created at the crescent shaped opening causes the fuel droplets to accumulate around the crescent shaped openings because of the greater viscosity of the fuel compared to the viscosity of the air, thus changing the atomization characteristics or the fuel-air mixture characteristics over those characteristics obtained from the fixed venturi. The conventional supply of idle fuel also alters the mixture during increased flow conditions. When the butterfly valve is rapidly opened, the air flow velocity through the venturi increases more rapidly than its main fuel discharge, which results initially in a lean fuel-air mixture. The accelerator pump attempts to counteract the initially lean mixture by injecting a stream of raw fuel into the airstream until the main discharge can supply sufficient fuel delivery for the increased flow. However, the raw fuel injection does not thoroughly mix or atomize with the air to provide the best combustible mixture.
The mixture alterations from a lean fuel-air mixture in some situations to a rich fuel-air mixture in other situations can rapidly occur during typical engine operation, as for example in the instance of an automobile being operated in commuter stop-and-go traffic. The inability to maintain the desired fuel-air mixture by the conventional carburetor under widely varying operating characteristics makes effective control over the pollutant emissions difficult or impossible, and also causes an adverse affect on fuel consumption economy. Certain of these factors are known and appreciated as significant problems in the prior art. Other of these factors may be more fully appreciated in view of the present invention, which is directed toward overcoming these and other problems in the prior art, and which is directed toward obtaining previously unobtainable benefits in improving fuel delivery apparatus and systems, particularly those for internal combustion engines which propel automobiles.